Thanks, however it was a capital v in B.

A=:'^<v>'
   B=:'<v>^'
   f=: 13 :'((|.|:|.4|+/~i.4),4|+/~i.4){y'
   f A
v<^>
<^>v
^>v<
>v<^
^<v>
<v>^
v>^<
>^<v
   B(-:"1) f A
0 0 0 0 0 1 0 0

Linda 

-----Original Message-----
From: programming-boun...@forums.jsoftware.com
[mailto:programming-boun...@forums.jsoftware.com] On Behalf Of bill lam
Sent: Tuesday, December 15, 2015 8:55 AM
To: Programming forum
Subject: Re: [Jprogramming] adventofcode day 3

to see why, try this
B="1 f A
On Dec 15, 2015 7:57 PM, "Linda Alvord" <lindaalv...@verizon.net> wrote:

> Why isn't the result  0 0 0 0 0 1 0 0 ?
>
> A=:'^<v>'
>    B=:'<V>^'
>    f=: 13 :'((|.|:|.4|+/~i.4),4|+/~i.4){y'
>    f A
> v<^>
> <^>v
> ^>v<
> >v<^
> ^<v>
> <v>^
> v>^<
> >^<v
>    B-:"1 f A
> 0 0 0 0 0 0 0 0
>
> Linda
>
> -----Original Message-----
> From: programming-boun...@forums.jsoftware.com
> [mailto:programming-boun...@forums.jsoftware.com] On Behalf Of David 
> Lambert
> Sent: Thursday, December 3, 2015 9:40 AM
> To: programming <programm...@jsoftware.com>
> Subject: [Jprogramming] adventofcode day 3
>
> Say P is a rank 2 list of 2D coordinates
>     4{.P
>   0 0
>   0 1
>   0 2
> _1 2
>
> Let's map the flight.
>
> NB. shift moves origin making minimum coordinates independently 0 NB. use:
> shift COORDINATES
> shift=: -"1 <./
>
> NB. grid generates an array of zeros large enough for only the 
> positive coords NB. use: grid COORDS
> grid=: 0 $~ >:@:(>./)
>
> NB. COORDS draw GRID  NB. color by number
> draw=: (i.@#@[)`(;/@:[)`]}
>
> load'viewmat'
> flight =: viewmat @: (draw grid) @: shift
>
> flight P
>
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